Circuit for water depth meter

ABSTRACT

A depth meter for use in water, which has a rotating disc carrying a light emitting diode that lights up to give depth indications. The rotating disc also carries a magnet which is used to generate a signal to initiate transmission of a high frequency signal through a crystal. The crystal receives any returned signal reflected from the bottom or an object in the water. The reflected signal is amplified, and a pulse discrimination circuit is used to determine if the amplified signal is acceptable. An acceptable signal trips a power circuit to a light emitting diode to indicate the depth of the bottom or object causing the reflected signal.

t o Unlted states Patent 1 [111 3,764,962 Bartel; Jr. Oct. 9, 1973CIRCUIT FOR WATER DEPTH METER 3,559,158 1/1971 Bettcher 340/3 R [75]Inventor: l(\liliigflles F. Bartel, Jr., Rosemount, Primary Examinerkichard A. Farley AttorneyRalph L. Dugger et al. [73] Assignee: Vexilar,Inc., Minneapolis, Minn. 22 Filed: Jan. 10, 1972 [57] AFSTRACT A depthmeter for use in water, which has a rotating PP N06 216,545 disccarrying a light emitting diode that lights up to give depthindications. The rotating disc also carries a [52] 5 c IIIIIIIIIIIIII I340/31, 340/3 magnet which is used to generate a signal to initiate [51] Int. Cl. 601s 9/68 transmission of a high frequency signal through aCrys [58] 1 n w of Search H 340/3 R 3 C 3 A tal. The crystal receivesany returned signal reflected from the bottom or an object in the water.The re- [56] References Cited flected signal is amplified, and a pulsediscrimination circuit is used to determine if the amplified signal isUNlTED STATES PATENTS acceptable. An acceptable signal trips a powercircuit 3,267,413 8/1966 Beebe et al. 340/3 R to a light emitting diodeto indicate the depth of the gzzif jr bottom or object causing thereflected signal. 6/1968 Halliday et a] 340/3 C 13 Claims, 5 DrawingFigures i M a 152 I I53 [451 Oct. 9, 1973 United States Patent [1 1Bartel, Jr.

PATENTED EU 9 973 SHEET 2 IJF 4 PAIENTEU BET 1973 SHEET 30F 4 PAIENIEU91975 3.764.962

- SHEET MJF 4 a A 4! MAG/VET PULSE IL A AMPLIFIER PULSE {5573 MASTER0400A [554 TEA/VSM/T TIME liField of the Invention The? presentinvention relates to circuitry for providing adequate transmission ofand insuring proper reception of reflected signals through a water depthindi- I cator crystal transmitter.

2.1 Prior Art Variousdepth indicators have been advanced in the artJandsome utilize a circuit that is initiated by a rotating ormoving magnetpassing over a coil. However, the pulse caused by the magnetpassing overthecoil is not greatly amplified in prior art devices, and this meansthat therpositioning of themagnet with respect to the coil, as well asthe quality of the magnets themselves -=has to be uniform in order toget a proper-signal each time the pulse: is delivered. In the presentdevice, the magnetic pulse is passed through an amplifier so that asaturated signal istreceived each time a pulse is deliv- *ered; andthesaturated signal is the signal that is used fortiming, and fortriggering the oscillator used for developing the transmitted signal. Bysetting thelevel of l the pulse; necessary to trigger the amplifierrelatively low,l the rspacing .of the magnet from the coil, the strengthof the magnet, and uniformity of the magnet P are not of particularsignificance as long as the minimu m jsignal required is generated.

SUMMARYOFTHE INVENTION A depth meterwhich utilizes a transmitted highfrefqtiencywsignal from a crystal transducer, and which re ceives areflected signal from a surface, such asthe bot- .1 tom or a fish, anduses the reflected signal to initiate indicating means to indicate thedepth of the surface causing the reflection.

The meter includes-a rotating discindicator device whichlrotatesbehind ameterpanel, and is driven by an electricmotor that is controlled at adesired speed. The

unityis made so that one rotation of the disc equals a known time. Asshownthe time cycle is sufficient to givedepth IIICIICEIIOI'SIIPEIIOabout 100 feet of water pt Theirotating disc carries a small magnet,that passes overl'aucoil on a circuit board positioned behind the disc,and this is used as a detector pulse to, at the zero positiom commencetransmision of a high frequency signalltransmitted by a crystaltransducer in the water,

"andwalsofor: initiating asignal of known duration used for asignal toother circuit components.

Thecrystal used transmits out the high frequency signalrland then alsoreceives any reflectedsignals, and

. generates an output fromthe reflected signal that is in turn amplifieiand is used for energizing alight emitting diode carried bytherotatingdisc, which will light up gwhen the reflected pulsetriggers the diode.The

This circuit includes theadditional feature of having a horn alertcircuit to indicate when the water is equal togor less than apreselecteddepth so that a boat operatorican receive a warning at the time ashallow bottom is beingapproached. This will aid docking of botas withrelatively deep draft, in shallow water.

Other objects of the invention will become apparent as the descriptionproceeds.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a sectional view of atypical meter housing having a rotating disc indicator operatedaccording to the present invention;

FIG. 2 is a front view of the meter device of FIG. 1;

FIGS. 3 and 4 are schematic representations of the depth indicatingcircuitry of the present invention; and

FIG. 5 is a timing diagram relationship graphically showing operation ofcertain portions of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, aninstrument housing 10 houses a water depth meter constructed accordingto the present invention, and the open face 11 of the housing issurrounded by a rim member 12. The rim 12 has stand off mounting members14 that in turn mount a circuit board 15 on which the circuit componentsto be described are mounted. Circuit board 15 has an electric motor 16mounted thereon, and the motor shaft 17 extends through the board 15,and mounts a rotating disc 18. The disc 18 is circular and when themotor 16 is running, rotates at a preselected speed, in the form shownapproximately 1440 revolutions per minute. The motor,and the circuitboard, are powered through suitable connections 20, leading to a batteryor other source of power 21 that can be remote power, or a battery pack.Rotating disc 18 carries two components utilized with thepresentinvention. These include a light emitting diode indicated at 23, mountedon the front face of the disc and aligned with an opening in the outercover of the meter so that when the light emitting diode lights, it canbe viewed, as shown at FIG. 2. The rotating disc 18 also mounts aceramic magnet 23 adjacent this outer edge,which is on the backside ofthe disc l8,-and this magnet, aswill be explained, is used forprovidinga triggering pulse for the circuit for initiating the operational cyclesfor the depth finder. The triggering pulse occurs when the magnet 23passes over a coil 24 mounted on the circuit board 15, and positioned toalign with the magnet during one portion of each rotational cycle of thedisc 18, as shown in the zero" depth position.

The depth meter is utilized with a transducer assembly 25, which has abarium titanate crystal 26 at its outer end. The transducer is connectedthrough a suitable jack 27 and cord 28 to other components on thecircuit board. The exact connection of course can be varied to suitexisting conditions. It should further be noted that power is carried tothe light emitting diode 22 through a slip ring type contacts which areindicated at 30 and comprise metal strips attached to the circuit boardI5, and which have outer ends that resiliently engage a metal ring onthe disc 18 so that power can be carried to the light emitting diode 22as the disc rotates.

The magnet 23 is a permanent ceramic magnet, and the magnetic fieldgenerated thereby will produce a signal in the coil 24 each time themagnet rotates past the coil.

In the operation of depth indicators, it has been known to utilizesuitable crystal transducers that are positioned in the water and aimedin the desired direction, and then transmit a high frequency signalthrough the crystal. The crystal is also used to receive the reflectedhigh frequency signal to energize a meter indicating depth. The elapsedtime between the transmission of the signal and the receipt of thereflected signal at the crystal indicates the distance from the surfacecausing the reflection to the crystal. The crystal transducers are wellknown in the art, and also various types of transmitters are well known.In the newer type depth indicators light emitting diodes are used asindicators but it has been found that the circuits presently used havegiven rise to various errors. First, the light emitting diodes may bemounted on the rotating discs, and light up once during eachrevolutionofthe disc in response to reflected signals to indicate thedepth. The transmission of the transmitted signal must be initiated at apreselected position of the disc, rather than on a regular time basis,because the rotational speed of the motor driving the disc can varyslightly. This means that for each revolution there must be some triggerpoint for transmission of the high frequency signal through the crystal.Then, too, there must be an adequate amplification of the reflectedsignal received back at the crystal; there must be ability to filter outnoise, and there also must be some assurance that the pulse or signalbeing used to energize the light emitting diode is a reflected pulse,and not noise.

Now, referring to FIGS. 3 and 4, primarily, a main on-off switch 31controls power to a main power line 32, which is at battery voltage, asshown 12 volts.

The power output along the main power line 32 is connected into voltageregulator circuitry as outlined in dotted lines at 33C so that there iscontrolled 7.5 voltage along a line 34. This level of voltage issubstantially below the normal battery voltage of 12 volts, and insuresthat as long as the battery has any life the proper controlled voltagewill be supplied to the critical components of the circuit, includingthe timing means and the pulse initiation means.

The voltage regulator for obtaining the control 7.5 volt line is showngenerally at 33C, and includes a zener diode 33, which is connectedbetween ground and the 12 volt line through a 390 ohm resistor 33D. Thevoltage between the zener diode 33 and the resistor 33D drives a diodebias network 33A, which in turn drives a pass band transistor 333 thatprovides current regulation to the line 34 for providing a substantiallyregulated 7.5 volt reference line to provide a regulation forfluctuation in battery potential and still have a known voltage levelfor giving accurate timing. The battery main switch also turns on themotor 16.

When the power switch 31 is on, assuming that the motor 16 is rotating,the circuit is energized, the disc 18 is rotating and the magnet 23 willpass over the coil 24 shown schematically at the upper left hand cornerof FIG. 3 and located in a pulse generating section outlined in dottedlines at 19. The coil 24 is connected between 7.5 volt line 34 andground, and is series connected with a 33K resistor 35, and a K resistor36. A high gain transistor 37 has its collector connected through a 6.8Kresistor 38 to line 34, and the emitter of transistor 37 is connectedthrough a 1.2K resistor 39 to ground. The base of the transistor 37 isconnected with a line 40 to a junction between the end of coil 24 andthe adjoining end of resistor 35.

The resistor selection for resistors 35 and 36 is such that the voltagealong line 40 is in the range of 2.5 volts. The transistor 37 comprisesa bias control amplifier.

Any increase or reduction of the voltage at the base of transistor 37will cause a corresponding increase or reduction of the potential at itsemitter. The transistor 37 is a high gain transistor, and when themagnet 23 moves past the coil 24, the magnet causes a momentary voltagepulse, that acts in opposition to the voltage on line 40, and reducesthe bias voltage to the transistor 37. This immediately causes a highgain on the collector side of transistor 37, and a pulse will be carriedon line 41 connected at a junction between the collector of transistor37 and resistor 38. Line 41 is connected to a ground line 42, through aseries combination of a first 220K resistor 41A and a 6.8K resistor 41B.

Referring to FIG. 5 momentarily, the wave form caused by the magnetpassing adjacent the coil 24 is illustrated at the top line at 44. Itcreates a negative voltage. The time the voltage appears is not of greatsignificance, as long as it reduces the bias to the base of transistor37 to cause the one shot master clock to operate.

The voltage at the collector of transistor 37 is normally in the rangeof 2 volts as shown, and when the magnet 23 causes the negative voltageform shown in FIG. 5 to be applied to the base of transistor 37 thevoltage on line 41 at the collector of transistor 37 will increase up tothe voltage on line 34, which is substantially 7.5 volts. Actually thegain of the transistor 37 is so high that if there was more potential online 34, it would be supplied along line 41. The form of the pulse atline 41 is indicated at 45 in FIG. 5. The pulse 45 is clipped so that ithas a square top, which represents the 7.5 voltage maximum on line 34.This positive pulse is supplied to the base of transistor 43, which isconnected to line 41 at a junction between the resistors 41A and 413.The pulse turns on the transistor 43 causing it to conduct through a 10Kresistor 43A from line 34 to its collector. The emitter of transistor 43is connected to the ground line 42.

Conduction of transistor 43 reduces the voltage at its collector causingan inverse or negative pulse along a line 46 connected to the collectorthereof and also connected to a capacitor 47 (as shown 0.047 microfarad)that is connected between line 46 and the base of transistor 48. Theemitter of transistor 48 is connected to the base of a transistor in aDarlington arrangement. The pulse on line 46 is illustrated at 46A inFIG. 5.

The master clock section which is outlined in dotted lines at 50includes the transistor 43, the capacitor 47, and transistors 48 and 49.In addition, the master clock includes a K resistor 51 connected betweenline 34 and the base of transistor 48 at a junction between thecapacitor 47 and the base. The master clock is a flipflop circuit, andonce the negative pulse appears on line 46 it pulls down one side of thecapacitor 47 immediately, and the potential build up of the capacitor 47through resistor 51 takes 4.0 milliseconds, during which time thetransistor 48 of course is turned off because of the drop to change thecapacitor 47. This provides a known state for transistor 48 and also fortransistor 49 for the length of time permitted by the RC network ofcapacitor 47 and resistor 51. The collector of the transistor 49 is heldhigh when transistors 48 and 49 are held off. This gives a known timeduration pulse on line 55 connected to the collector of transistor 49.

The negative pulse appearing on line 36 from the collector of transistor43 is on the order of 2.0 milliseconds, and the exact time of this pulseis not critical. The master timing clock portion 50 then provides a4.0ms

negative pulse along the line 55, that is used through junction A forother components to be explained. This pulse is shown at line 55A inFIG. 5. The line 55 also is connected through a 220K resistor 56 to thebase of transistor 43.

Thenegative pulse 45 appearing on line 46 is also carried alonga linethat is connected to a 0.018 microfarad capacitor 57 forming a portionof the oscillator drive .and crystal transmitter section indicatedgenerally.1at,.59. The pulse online 46 further is carried along the line60A to a motor control that will be further explained.

The capacitor 57 is connected to a resistor 58 that is in turn connectedbetween the line 34 and the base of a transistor 59.The emitter oftransistor 59 is connected to the base of a transistor 60 forming thecontrol for the oscillator circuit which is generally indicated at 6l.llThe oscillator circuit can be of any general design, and includes atransistor 62 and diodes 63, that provide for control and for currentstabilization when the control signalafrom the transistors 59 and 60 isturned off to quickly stop the oscillation of the oscillator. Thetransformer providesthe tank circuit for the oscillator and crystaltransmitter. The output winding 65 of the transformer is connectedacross the crystal 26 that is shown schematically in the drawing. A 1600picofaradcapacitor 66 is utilized for tuning purposes across thecrystalas well.

The negative pulse on line 46 drops the potential on capacitor 57, andthe charging of the capacitor through the. 150K resistor 58, takes 1.8milliseconds at the potenti'al on line 34. The operation of this RCcircuit regulates the time of transmission of the signal from theoscillator. During this time, the transistor 59 is shut off,

theitransformer so that the oscillator develops 200 Ki lohertzKKl-lz)200 volt :peak to peak output signal across the transformer outputwinding 65. This signal is transmitted by the crystal 26 into the water.The oscillator section 59 transmits for [.8 ms controlled by the RCcircuit 57 and 58. Referring again to FIG. 5, at

70, 1the 1.8 mspulse is illustrated in the time graph. This 1.8 ms pulseis the time of transmission, and in line 71, there is illustrated the200 volt peak to peak 200 KHZ signal 71 which is transmitted.

It might be mentioned at this time that the transmitted signal will bepicked up by the rest of the circuitry, and will cause the lightemitting diode 22 to light, because the transmitted pulse will ringthrough the circuit; and the. light will light at a zero point where themagnet 23 crosses the coil 24. The magnet 23 crosses the: coil 24approximately every 43 ms, (plus or minus 1 ims)vso each cycle ofoperation repeats at that frequency.

Once the signal has been transmitted by the crystal, and .theoscillatorshut off, any reflected return signal will then be picked up by thecrystal 26. This causes the crystal to deliver an outputsignal through a300 picofared. AC pick off capacitor 75. This crystal output is receivedby the input of first stage of a three stage amplifier. These stages areoutlined in dotted lines at 76, 77 and 78. Because the type of amplifieris a matter of choice by the designer, the construction of theamplifiers will not be explained in detail. It should be noted that eachof the amplifier sections has a resistorcapacitor series connectionacross the lines to de Q" and decouple the amplifier from the lines toprevent interference from high frequency signals that might besuperimposed in the line. The first such arrangement is shown at 79, andincludes a 100 ohm resistor and a 0.0l microfarad capacitor, for thesecond stage 77, there is a line 80 including a 10 ohm resistor and a0.001 microfarad capacitor, and the line 81 is coupled across the powerlines with the same value resistor and capacitor as in line 80. Firstand second stage amplifiers are bandpassed amplifiers in order to reducethe amount of noise and to give some shaping to the reflected signalreceived by the crystal. The second stage includes a transformer 82 thatis tunable so that it can be peaked for maximum return signal.

The secondary of the transformer 82 is connected through a 5Kpotentiometer indicated at 83 that is the sensitivity adjustment, andthe wiper 84 is coupled to the main on-off switch so that thesensitivity of the output can be manually adjusted by rotating theon-off switch.

The output of the third stage amplifier 78 is connected through a line85 to the input of an emitter follower transistor circuit outlined at86. This gives current amplification for the voltage signal coming fromthe output of amplifier 78. The same voltage level signal is coming outof the circuit along the line 87 as is put in, except it has a higherdrive capability. The emitter follower 86 includes a transistor 88, thebase of which is controlled by the output of amplifier 78. A suitable100 ohm resistor 88A is connected between the collector of transistor 88and the power line, and a 10K resistor 88B is connected between theemitter and ground. The resistors 88C and 88D connected between thebattery voltage line and base, and ground and base respectively are both10K resistors. The line 87 has a 0.001 microfarad capacitor 87A therein,and this line 87 in turn is connected into a signal detector stageindicated generally at 90 by dotted lines. The diode 91 in line 87provides a return for AC signals from ground. Line 87 is connected tothe base of a transistor 92. A resistor 93 coupled between the base oftransistor 92 and ground keeps the transistor 92 turned off when thereis no return coming from the amplifier stage along line 87. Thecollector of the transistor 92 is connected to a 7.5 volt line through apair of series connected 2.7K resistors indicated at 94.

The collector of the transistor 92 is connected with a line 95 to ajunction between a pair of series connected 2.7K resistors 96, that areconnected between the controlled voltage line 89 and a 5.4K resistor 97that in turn is connected to ground. In addition, the line 95 isconnected through a 0.047 microfarad capacitor 98 to ground. Theresistors 96 and 97 form part of a pulse discriminator circuit outlinedin dotted lines at 99.

The pulse discriminator includes a PNP transistor 100 which has itsemitter connected through an 82K resistor 101 to a line 89, and itscollector is connected to a collector of an NPN transistor 102 that hasits emitter in turn connected to ground. The base of the transistor 100is connected to the junction between the two resistors 94, and the baseof transistor 102 is connected to the junction between resistor 97, andthe adjacent series resistor 96. The collector of transistor 102 is alsoconnected through a 0.047 microfarad capacitor 103 to ground.

The light emitting diode power driven circuit outlined in dotted lines 1includes a transistor 105 which has its collector connected through a1.2K resistor 106, and a 10K resistor 107 to the battery power line. Thebase of transistor 105 is connected through a 150 ohm resistor 108 tothe collector of transistor 102.

A pair of Darlington arranged transistors are included in this circuit,and include a PNP transistor 1 10, having its base connected to ajunction between resistors 106 and 107, and its emitter connectedthrough an induction coil 1 1 1 to the battery potential line. Thecollector of the transistor 110 is connected to the base of an NPNtransistor 112. The collector of transistor 112 is connected to one endof coil 111 at a junction with the emitter of transistor 110 and theemitter of transistor 112 is connected through an 8.4 ohm resistor 113to the light emitting diode 22. The diode 22 is also connected toground.

When either a transmitted or reflected 200 Khz signal appears on line 87and is of proper level, the transistor 92 is turned on during thepositive half cycle of the signal. The transistor 92 operates to clipthe positive voltage at 0.6 volt because this is the base to emitterdrop of the transistor 92. In a negative half cycle, the collector oftransistor 92 is held low through the action of capacitor 98, so thatthe collector is held near ground or just slightly above groundpotential whenever there is a signal at its base.

When the collector of transistor 92 goes low the potential at thejunction between the two resistors 94 will drop to a voltage level thatis substantially one half of the difference between the voltage at thecollector of transistor 92 and the voltage along the 7.5 volt line 89.This signal is used in the pulse discriminator section indicated at 99in dotted lines, and is applied to the base of the PNP transistor 100.The lower voltage at the base of transistor 100 causes the transistor100 to be turned on and conduct.

Because the junction between the resistors 96 has ben pulled down toapproximately ground potential due to the reduction of potential of thecollector on transistor 92, the potential at the base of transistor 102,

which is connected between the resistor 97 and the ad-' jacent resistor96, is reduced to a point where the transistor 102 is turned off. Thismeans that the signal carried through transistor 100 now is appliedacross the capacitor 103 through junction 103A to charge this capacitor.The resistors 97 and 96 are utilized to insure that the potential on thebase of transistor 102 is sufficiently low to turn off this transistor.The resistor 101 between the line 89 and the emitter of transistor 100insures that there is a substantially uniform current flowing throughthe transistor 100 to charge the capacitor 103 when transistor 102 isturned off. This capacitor 103 then charges, and the voltage appearingat the junction 103A builds up on a ramp function with respect to time.When the potential level at 103A reaches 1.2 volt, the transistor 105 isturned on and the voltage level at 103A is clamped at 1.2 volt, which isthe base to emitter drop of transistor 105. The capacitor 103, which asshown is 0.047 microfarads, is selected so that the charging time toreach 0.6 volt is approximately two-thirds of the normal transmit time.The transmit time is l.8 milliseconds, and of course then the reflectedsignal coming back to the crystal indicating depth also is beingreceived for 1.8 ms. Therefore the charging ramp time for capacitor 103to reach 1.2 volts would be approximately 1.2 ms. lf before the junction103A has reached its logic level of 1.2 volt, the signal on line 87disappears so that the transistor 92 is turned off, the transistor 102will again immediately turn on and there will be a dead short appliedacross the capacitor 103. The voltage across this capacitor 103 willdrop out within a microsecond or so. That means that if the pulse orsignal received along line 87 is less than 1.2 ms, transistor 105 willnot be turned on even though the discriminator circuit 99 will start tofunction. For example if the signal on line 87 is only approximately 0.8ms the capacitor 103 will start to be charged, but when the signal online 87 ends the transistor 92 would be turned off, and this throughline and transistor 102 would immediately discharge the capacitor sothat junction 103A would not reach the logic level and transistor 105would not be turned on.

Assuming that signal of proper time has appeared so that the voltage onthe base of transistor 105 has exeeded the 0.6 volt necessary to turnthis transistor on, this transistor acts as a current sink andimmediately starts to conduct current from the bzttery line to groundthrough the resistors 106 and 107, which act as a voltage dividernetwork. The voltage drop across resistor 107 in relation to resistor106 (which are 10K and 1.2K respectively), causes the base of thetransistor 110 to reduce in potential, turning this transistor on andcausing conduction by the transistor. When the transistor 110 conducts,transistor 112 is turned on. The current gain is through the transistor110, which is an PNP transistor, and the power drive is through theemitter follower transistor 112. Current is conducted through the coil111 from the battery line, through transistor 110, and through an 8.5ohm wire wound resistor to the light emitting diode 22, causing the LEDto light up for the time of receipt of the signal along line 87 as longas this signal is on for greater than 1.2 ms. The resistor l 13 on theinput of the light emitting diode 22 is for providing a voltage dropdown to the required 2.7 volts for the LED. The coil 111 is to give somecontrol to the current wave form because the light emitting diode drawsa tremendous current as soon as it is turned on, and the coil providessome retardation or roll off of the current signal.

Thus there are two locations in each revolution of the rotating disc atwhich the light emitting diode will light up. One is that at the zeropoint when the magnet 23 passes over coil 24, and the initialtransmission rings through the circuit to light up the diode 22. Theother is when the reflected pulse is received by the crystal, whichreflected pulse is amplified through the amplifier system, and passedthrough the pulse discriminator to light the diode 22. The pulsediscriminator 99 filters out any extraneous noise of short duration, sothat a sustained pulse of at least 1.2 ms is necessary to turn on thelight emitting diode.

The main power circuit has a voltage meter thereacross and include asuitable resistor and adjustable potentiometer so that the voltage ofthe battery being used can be indicated visually to an operator.

The drive for the motor 16 can be of any desired configuration to give arelatively well governed motor 1 the line for filtering out noise. Thefilter capacitor 128 is on the order of 300 microfarads, and a 6.8microfarad .filtercapacitor 129 is also applied across the motor 16 forfiltering. I

When the magnetic kicker signals are supplied along line160A, they areapplied through a kicker circuit 130, that has a control transistor 133.The capacitor 131 is charged through a diode .132 each time the negativepulse from line 60A is applied to transistor 133. This providesna signalto a pair of transistors in a voltage control circuit outlined by dottedlines at 134. This circuit providesa control voltage to the motor drivecircuit from the line 34. A potentiometer is provided on the collectorof the second transistor for speed adjustment: The area indicated indotted lines at 1348 operatesfrom the control voltage out of area 134and is merely a current amplifier utilizing two PNP transistors whichcontrol the main power transistor 134A. The main power transistor 134Ais in the motor drive circuit outlined at.l37, which provides the outputof the two darlingtons-134B into the motor so that a fixed voltage. isprovided that holds the motor at a suitable rpm:

Again, if desired, the motor may be mechanically governed instead ofusing the kicker circuits shown.

The circuit just described leading up to lighting of the LED,includingthe pulse discriminator, and the motor drive circuit is all.that is essential for operation of the present invention. The novelfeature of having a moving: magnet that generates a pulse that can bevarying in length and duration and strength, but still will give a.highly' amplified signal utilized for running RC circuitsfor fixed timegeneration, makes the unit very accurate even with mechanical variationsin assembly. However, in addition to the visual light signal, it is inmany instancesdesirable and even necessary to include an audible signalthat is sounded when a certain depth or less is being indicated by theLED. An indicator is set to give a sound at a particular depth or less,so that when the return is coming from the bottom of a body ofwaterindicated that the bottom is getting close, an operator can makenecessary changes to avoid running aground in a boat, and also thisgives an indication of rocks and the like.

Referring to the bottom portion of FIG. 3, it can be seen that the 12volt (battery) line 150 is connected nected through a suitable link 152to a potentiometer which will be explained later. In addition, a line153 is connected with a 0.22 microfarad capacitor 154', and a68K-resistor 155 to the ground line 42. Line 153 in turn :is alsoconnected to the base of a transistor 155, which is shown in dottedlines, and is connected across the junctions for transistor 105, andwould receive the same signals at its collector and emitter. Thistransistor 155 is an alternate transistor used when the horn or alarmcircuit to be described is utilized, and for the purposesofthediscussion, it can be considered to be in the circuit as shown. Asuitable 68K resistor 156 also connects between line 153 and groundadjacent the base of transistor 155.

The line 153 has a 10K resistor 157 therein, and a switch 158 connectedto the link 152 for the rotary onoff switch. The rotary on-off switchalso has push pull capabilities, with the same link 152, and the switch158 is operated on a push pull basis. Therefore, lines and 153 extend tothe additional circuit. A controlled voltage (7.5) volt line 159 is alsoconnected to the additional circuitry shown in FIG. 4 and 12 volt(battery) line 160 is connected down to the circuit at FIG. 4 which nowis specifically referred to.

The audible signal requires a suitable time ramp generator shown indotted lines at 149 that is independent of the other portions of thecircuit, and which can be used for giving a signal output when the timeelapse from initial start of a transmission signal so that when thereturn is received it would indicate a particular depth. The power line160 is connected across a type 741 operational amplifier indicated at165. This amplitier is an integrating operational amplifier having andifferential input, and providing. an output that is normally a rampfunction. The amplifier is powered across the battery line, and one ofthe inputs terminal thereto is connected with a 10K resistor 166 to thejunction between another pair of 10K resistors 167 and 168 from the line160 to ground. The other input terminal for the operational amplifier165 is connected through a 220K resistor 169 to the ground line 42, andis also connected through a feed back 0.22 microfarad capacitor 170 toits output line 171. The capacitor 170 provides the output rampgenerating function, and as can be seen, the line carrying the capacitor170 is connected at a junction between the resistor 169 and the inputterminal of the amplifier.

in addition, a transistor 172 is connected across the 0.22 microfaradcapacitor 170. The base of the transistor is connected with a line 173through a suitable resistor to junction A, which carries the 4.0 mspositive pulse signal from the collector of transistor 49. When the 4.0ms signal appears on line 173, the transistor 172 conducts, shorting outthe capacitor 170 and causing the operational amplifier 165 to againstart its ramp output function when the signal on line 173 is removed.

Referring to the line 174 in FIG. 5, during each time period cycle the4.0 ms signal is the flat portion of this line indicated at 174A. Thisis when the capacitor 170 is shorted out, and there is a low output fromthe operational amplifier 165. This time period of 4.0 ms equalssubstantially five feet of depth, (it includes the signal transmissiontime of 1.8 ms) so during this time when the depth is 5 feet or less,the audible signal cannot be set. After this point, on the graph, thevoltage output of the amplifier 165 generates a ramp function toward itspeak which is reached when the signal again appears at junction A. Theslope of the ramp 1748 will be determined by the size of the capacitor170. Then, as the 43 ms period has expired, the signal will again appearat junction A and the output will be shorted, dropping down as shown tothe right of FIG. 5. The operational amplifier 165 is provided with anartificial or synthetic ground through the use of the resistors 166, 167and 168. The potential is actually above ground, so that the actualvoltage level at line 174A would be approximately onehalf of the batteryvoltage.

The output of the amplifier 165 on 171 is fed into one input terminal ofa second type 741 operational amplifier 175. The amplifier 175 ispowered by the power line 160, and the second input terminal of theamplifier 175 is connected to a wiper 176 of a set point adjustmentpotentiometer 177 that is controlled by the mechanical link 152. One endof potentiometer 177 is connected through a 1.2K resistor 178 to theline 160 and the other end is connected through a trim potentiometer 179and 5.6K resistor 180 to ground. The trim potentiometer 179 is a factoryadjustment that is to trim up the settings of the unit so that properresponse is achieved. The potentiometer 177 is the set pointpotentiometer which is manipulated by the operator of the depth meter toadjust the depth at which the sound signal will occur. The amplifier 175is an open loop gain amplifier, and delivers an output along its outputline 181 whenever the voltage on line 171 (one input to amplifier 175)exceeds the voltage on the set point line potentiometer wiper 176 whichis the other input to amplifier 175. When the voltages at the inputterminals are equal there is no output along line 181.

The voltage at the input terminal connected to line 176 can be adjusted,and whenever the ramp voltage along line 171, which is represented atline 174 in FIG. exceeds the level on line 176 you get a immediateoutput along line 181. This is illustrated generally at 185 in FIG. 5for one set point condition where the set point level equals the voltageat starred point 184A on graph line 174B. The operational amplifier 175actually is a change of state amplifier and gives a square output signalalong line 181.

Thus, in the ramp generator outlined in dotted lines in 149 in FIG. 4 atime-voltage function is being generated. The set point comparatorcircuitry just described is indicated at 186 in FIG. 4. The nextcircuitry indicated at 187 in FIG. 3 comprises set point indicatorcircuitry. The square wave output along line 181 is utilized for twodifferent functions, and as shown, the output on line 181 is appliedthrough a 56K resistor 188 to the base of a transistor 189. This causesthe transistor to conduct due to the output from amplifier 175, droppingthe potential at the collector of the transistor, and giving a positivepotential at the emitter, this is connected to an RC network comprisinga K resistor 190, and a 0.01 microfarad capacitor 191 connected to thebase of a second output transistor 192. When the transistor 189 conductsthis will cause the collector of transistor 193 to give a positiveoutput signal. The area 187 comprises a logic shift network as a setindicator, and the positive output along line 153, which is connected tothe collector of transistor 192, assuming that the push pull switch 158in FIG. 3 is closed will be transferred along the line 153 to the baseof the transistor 155. This will cause the transistor 155 to conduct,and in turn energize the circuit to power the LED 22 in the same manneras when the transistor 105 conducts. The output along line 153 lastsonly as long as it takes for the RC network 190, 191 to build up thepotential on the base of transistor 192, as shown at 193 in FIG. 5, thisis about 0.6 ms.

The lighting of the light emitting diode through the push pull switch158, when the set indicator has an output, will illuminate the lightemitting diode in the proper angular position during each revolutionthereof. This lighting indicates the maximum depth at which the horncircuit will be activated (the horn is also activated at shallowerdepths). Thus the operator can adjust the set point by rotating thecombination switch driving the link 152 until the light emitting diodelights and indicates the maximum depth at which the operator wants asounding. If the operator wishes, the light emitting diode can be leftin the circuit for the set indicator so that it will light up at thedepth where the sounding will occur during each revolution, and willalso light up when each transmitted pulse is returned. Assuming that anoperator had the set point indicator set for 60 feet (the indicator isset up for foot depth maximum) and had the push pull switch 158 on, andalso assuming that the operator was operating in 80 feet of water, thelight emitting diode would light at the zero point, as previouslyexplained, it would light at the 60 feet point because of the outputfrom the set indicator along line 153 to the transistor 155, and wouldalso then light at the 80 foot point because of the reflected signalcoming through the crystal transducer energizing the light emittingdiode through the detector circuitry, the pulse discriminator circuitry,and the power circuitry for the light emitting diode. Then as the boatapproached the 60 foot depth, the .visual dots for the light emittingdiode would gradually move closer together, and then when the returncame at the 60 foot point the lights would merge.

The circuit area outlined in dotted lines at 195 also comprises a logicconversion. The logic conversion circuitry includes the B terminal orjunction input shown in FIG. 3 above the LED, and this carries a signalwhen the LED is turned on. In addition the output of amplifier throughline 181 is applied through a 56K rcsistor 196 to the base of atransistor 197, which is of the PNP type. Thus when the signal from theline 181 appears at the base of transistor 197, the collector, which isconnected through a suitable resistor to ground, will go low, and line198 connected to the collector will be at a low potential. Line 198connects through a 56K resister to a line 199. The pulse at junction A,which is the 4 ms pulse, appears along a line 200 which connects througha 56K resistor to line 199.

A line 201 coupled to the B junction is connected through a 10K resistorto the base of a transistor 202, and through a 68K resistor to ground.The collector of the transistor 202 isconnected through a 10K resistorto the line connected to theem'itter of transistor 197, and this is thebattery line. The collector of transistor 202 is connected through a2.7K resistor 203 to line 199, on the opposite side ofa 56K resistor 204from the base of a transistor 205, to which the line 199 is connected. A.047 microfarad capacitor 206 is connected to the junction betweenresistors 203 and 204 and to ground.

When there is a positive signal on line 201 due to lighting of the diode22, transistor 202 will conduct, causing its collector to go low.Likewise, when there is an output from the amplifier 175 there is a lowpotential along line 198, and when the 4 ms signal has disappeared fromthe line 200, the base of transistor 205 is therefore at a low level andthe transistor is not conducting. However it should be noted thatwhenever the light emitting diode 22 is not powered, the transistor 202will be turned off causing a high potential on the base of transistor205 through the line 199, resistor 204, resistor 203, and the resistorbetween the collector of transistor 202 and the battery line, which willcause the transistor 205 to conduct.

The transistor 205. is in a circuit area indicated in dotted linesthattcomprises a three input NOR gate 207 so thatwif any of the threeinputs to line 199 are high, the transistor 205 will conduct. When thethree inputs to the three input NOR gate 207 are all low, the transistor205 is cut off, and the potential in the collector of transistor205,-which is connected to the 7.5 volt line 159 through a suitable 39Kresistor 208, goes high. The collectorof transistor 205 is connecedthrough a suitable 50K resistor 209 to the base of a transistor 210.When the potentiahat the base of transistor 210 goes high because oftheturning off of the transistor 205, the tran sistor 210 will conductcausing its collector to go low. The collectorof transistor 2l0 isconnected through a K resistor211 to the 7.5 volt line 159 and isconnected to a 0.22 microfarad capacitor 212 that in turn hasitsotherside connected to the base of a transistor 213 and through a 680Kresistor 214 to the 7.5 volt line. :Thetransistor 213 is connected tothe base of another transistor 215. The collectors of transistors 214and2l5 are each connected through suitable resistors to the 7.5 voltline, and the collector of the transistor 2151s also connected through a56K resistor 216 back to :the base of transistor 210.

When the collector of transistor 210 goes low becauseiof turning on-oftransistor 205 it changes the potentialto capacitor 212, and theresistor 214 and capacitor 212 form a timing clock which turns off thetransistor 2135 for a time approximately equal to three of thetransmitted pulse periods, or approximately 139 ms. This causes thecollector of transistor 215 to go highamaking a signal appear throughresistor 216 back to the base of transistor 210, keeping the transistor210 conducting for this period of time. All the while that a thetransistor 210 is conducting, a line 217 is connected termined by thecapacitors 226, which as shown are 0.047 capacitors and the resistors227 which'as shown are 33K resistors.

The output of the tone generator 225 is applied along the. line 228through a 56K resistor to the base of a transistor 229. Another 56Kresistor 230 is in line 217. Any; signal on line 217 keeps thetransistor 229 turned on whenever the transistor 210 is shut off.However, when the output from the collector of transistor 210 goes 101w,the signal along line 228 is effective to controlthe transistor 229.When the transistor 210 is shut off, the collector of transistor 229stayed low, because the transistorwas conducting due to the signal fromline217. Themwhen the signal at line 217 goes low, the transistor 229alternately conducts and is shut off in accordance with the 500 cyclesignal on line 228. This pulsating will cause the transistor 240,comprising the speaker drive transistor to also alternately turn on andoffbecause the base thereof is connected to the collector of transistor229 through a suitable resistor 241. The collector of transistor 240 isconnected to the battery: linethrough a l.2K resistor 242, and a 10Kresister 243.The base of a PNP transistor 244 is connected to a junctionbetween resistors 242 and 243, and the collector of this transistor 244is connected to the base of a power transistor 245 which drives throughthe speaker coil 246 through a suitable resistor (approximately 12 ohm)247. This speaker will be driven at the 500 cycle frequency to give itaudible signal for the length of the speaker timing clock circuit 219which is approximately 139 ms. This in turn is long enough so that it isaudible to the human ear. Shorter periods of sound are hard to discernby humans.

In the graph representation 251 on FIG. 5 a window formed by the lack ofthe operational amplifier 175 is illustrated during the first part ofthe cycle for each period. This window illustrates the time during whichthe horn will sound if a return is received. A return, which powers theLED gives a pulse at junction B indicated at 250. Since the 4 ms signalon line 200 has disappeared the potential on the base of the transistor205 will be low, the NOR gate will trip to set off the time clock 219,to initiate the speaker, indicating that a return has been received at adepth equal to or less than the set point depth. The speaker sounds fora length of time sufficient to be identified by the human ear. Ofcourse, once the time clock 219 is reset, any more returns will againset it off so that in water of less depth than the set point asubstantial continuous sound will be heard.

A push pull switch also is tied in with the rotary switch 31, andenergizes a light circuit 261 to provide a night dial light when usingthe unit in night time operations.

The on-off switch 151 can be used for disabling the horn and set pointcircuit if desired.

The unit is reliable and accurate in arotating disc in dicator. Themagnetic pulse keeps the calibration accurate without precise control ofmotor speed, because only one transmission occurs during each motorrevolution.

What is claimed is:

l. A depth indicator device for use in water comprising transducer meansfor transmitting a first signal through the water, said transducer meansreceiving reflected return signals when said first signal is reflectedfrom surfaces, circuit means powering said transducer means, saidcircuit means including rotating drive means, signal means carried bysaid rotating drive means, and means to sense position of said signalmeans at each revolution of said rotating drive means and to deliver acontrol signal therefrom including high gain amplifier means foramplifying the control signal from said signal means, said high gainamplifier means providing an output pulse, a signal transmitting circuitconnected to said transducer, transmitting timing means connected to beresponsive to said output pulse and connected to control saidtransmitting circuit, said output pulse triggering said transmissiontiming means to cause the transmitting circuit to transmit a selectedsignal through said transducer means into the water for a length of timeset by said transmission timing means, said selected signal reflectingto provide a reflected return signal to said transducer means afterstriking a surface, second amplifier means having an input connected toreceive reflected return signals from said transducer means and havingan output providing an amplified reflected return signal, detectormeaiis for detecting signals at the output of said second amplifiermeans, signal discriminator means for determining the duration ofsignals at the output of said second amplifier means in relation to apreselected time period, said signal discriminator means rejectingsignals of less than said preselected time duration, indicator meansconnected to the output of said signal discriminator means, saidindicator means including power drive means for driving an indicator toindicate when a reflected signal has been received by the transducer andwhich has not been rejected by said signal discriminator means duringeach revolution of said rotating drive means.

2. The combination as specified in claim 1 wherein said indicator meanscomprises a light emitting diode means, and said power drive meanssupplies current to said light emitting diode means.

3. The combination as specified in claim 1 wherein said circuit means ismounted onto a circuit board, and said rotating drive means comprises adisc-like member rotating substantially parallel to and adjacent saidcircuit board, said signal means comprising a magnet mounted on saiddisc member, and said means to sense said signal means comprising a coilmounted on said circuit board positioned in the annular path of saidmagnet and in position wherein the magnetic field from said magnetpasses across said coil as said disc rotates to generate said controlsignal.

4. The combination as specified in claim 3 wherein said high gainamplifier means for said control signal comprises a bias controltransistor having a collector, emitter and base, means providing anormal bias voltage on the base of said transistor, and said coil beingconnected in the circuit to the base of said transistor whereby voltagegenerated in said coil by passage of the magnet adjacent said coil is inseries opposition to the voltage normally on said base and whereby thecollector of said transistor raises in potential when a voltage isgenerated in said coil.

5. The combination as specified in claim 4 wherein said means providinga transmission of signals through said transducer comprises a highfrequency oscillator, and drive means to said oscillator, said drivemeans including a first resistance-capacitor timing clock network, thechange in potential at the collector of said bias control transistortriggering action of said first resistance-capacitance network.

6. The combination as specified in claim 1 and means to deliver asecondary signal when the return from said transducer is less than apreselected time after the transmission of the first signal through saidtransducer means, said means to deliver a secondary signal includingmeans to generate a signal proportional to the time after ceasing thetransmission of said first signal through said transducer, comparatormeans to compare the signal generated by said means to generate saidproportional signal with a selected signal level, three input gate meansdelivering an output signal whenever transmission of said transmittedsignal has ceased and the signal discriminator gives an output prior tothe time when the signal from the means delivering said signalproportional to time equals said comparator signal, and separateindicator means connected to the output of said gate means to give anindication when the gate means delivers an output.

7. The combination as specified in claim 6 wherein said separateindicator means comprises an audible signal, and means connected to theoutput of said gate means to lock said audible signal on for a length oftime sufficient to be discerned by human ear.

8. The combination as specified in claim 6 wherein said means to developa signal proportional to time comprises an operational amplifier havingan output proportional to the difference between two inputs, a feedbackconnection between the output of said amplifier and one input thereto,capacitance means in said feedback connection to cause generation of anoutput voltage function from said amplifier means, and means to shortsaid capacitance means for a preselected length of time during thetransmission of a signal through said transducer at the start of eachcycle of said rotating drive means.

9. The combination as specified in claim 8 wherein said comparator meanscomprises a second operational amplifier having differential inputs andan open loop gain output, one of the inputs to said second operationalamplifier being connected to the output of said first operationalamplifier, and the other input of said second operational amplifierbeing connected to an adjustable voltage source.

10. The combination as specified in claim 9 and means connected to theoutput of said second'operational amplifier effective to deliver asignal energizing said first indicator means for a preselected length oftime whenever the second operational amplifier first delivers an outputsignal.

1 1. In a water depth meter including means for transmitting signalsthrough a transducer and receiving reflected signals from a surfacereflecting said transmitted signals, first means to indicate when thereflected signals are received in relation to the time when thereflected signals were first transmitted through said transducer, andsecond means to give a warning when a signal is returned lessthan apreselected time after the transmission of said signals through saidtransducer, said means to give said warning comprising a firstoperational amplifier, said first amplifier having a differential input,and one of said inputs being connected through a capacitance feedbackloop whereby the output of said operational amplifier is a straight linevoltage function in relation to time, means to initiate said voltagefunction at a preselected time in relation to the initiation oftransmission of said transmitted signal, and comparator means todetermine when said voltage function reaches a preselected levelcomprising a second operational amplifier having an open loop gainoutput and a differential input, a first of the differential inputs tosaid second operational amplifier being con nected to receive the outputfrom said first operational amplifier, and a second of said inputs tosaid second amplifier comprising an adjustable voltage source means, andmeans to deliver a warning when a reflected signal has been receivedbefore the comparator means delivers an output.

12. The combination as specified in claim 1 and second means to operatesaid first means comprising a timing circuit tripped by an output ofsaid second operational amplifier operable to operate said first meansfor substantially the same period of time as a reflected signal operatessaid first means.

13. The combination as specified in claim 11 wherein said firstmeans'comprises a light emitting means, a rotating disc means carryingsaid light emitting means, and means to initiate a transmission of saidtransmitted signal at a preselected position during each rotation ofsaid rotating disc means, comprising a magnet member and a coil member,one mounted on said rotating disc and the other spaced from and fixedwith respect thereto, the magnet and coil being positioned to deliver acontrol signal each time the rotating disc rotates one revolution.

23 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,7641962 Dated October 9, 1973 Inventor(s) Charles F. Bartel, Jr.

It is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

Column 1, line 66 "botas" should be --boats--. Column 6, line 16"bandpassed" should be --band passed--. Column 14,

line 28 "160" should be --260-'-; Column 14, line 53, (Claim 1,

line 14) "transmitting" should be --transmission--. Column 15,

line 4,(Claim 1, line 32) "duration" shouldbe --period--. Column 16,line 5, (Claim 8, l'ine'S) after "said" insert --operational--;

Column 16, line 8', (Claim 8, line 8) before "amplifier" insert--operational--; after "amplifier" cancel --means-- (first occurrence);Column 16, line 17, (Claim 9, line 6) before "operational" insert--mentioned--; Column 16, line 23, (Claim 10, line 4) after "first"insert --mentioned--; Column 16, line 52, (Claim 12, line 1) "1" shouldbe --11--.'

Signed and sealed this 16th day of April 19m.

(SEAL) Atte st:

EDWARD M.FLETGH}E,JR. 0. I iARsHALL DANN Attesbing Officer Commissionerof. Patents 7 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTIONPatent NC. 3,7641'962 Dated October 9, 1973 Inventor(s) Charles F.Bartel, Jr.

It is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

Column 1, line 66 "botas" should be --boats--. Column 6, line 16"bandpassed" should be --band passed--. Column 14, line 28 "160" shouldbe --260-'-;- Column 14, line 53, (Claim 1, line 14) "transmitting"should be --transmission--. Column 15, line 4, (Claim 1, line 32)"duration" should be --period--. Column 16, line 5, (Claim 8, line 5)after "said" insert --operational--; Column 16, line 8, (Claim 8, line8) before "amplifier" insert --operational--; after "amplifier" cancel--means-- (first occurrence) Column 16, line 17, (Claim 9, line 6)before "operational" insert --mentioned--; Column 16, line 23, (Claim10, line 4) after "first" insert --mentioned--; Column 16, line 52,(Claim 12, line 1) "1" should be --11--,

Signed and sealed this 16th day of April 197E;

(SEAL) Atte st:

EDWARD M .FLETGHER JR p C MAR SHALL DANN .Attesting Officer 1Commissioner of Patents

1. A depth indicator device for use in water comprising transducer meansfor transmitting a first signal through the water, said transducer meansreceiving reflected return signals when said first signal is reflectedfrom surfaces, circuit means powering said transducer means, saidcircuit means including rotating drive means, signal means carried bysaid rotating drive means, and means to sense position of said signalmeans at each revolution of said rotating drive means and to deliver acontrol signal therefrom including high gain amplifier means foramplifying the control signal from said signal means, said high gainamplifier means providing an output pulse, a signal transmitting circuitconnected to said transducer, transmission timing means connected to beresponsive to said output pulse and connected to control saidtransmitting circuit, said output pulse triggering said transmissiontiming means to cause the transmitting circuit to transmit a selectedsignal through said transducer means into the water for a length of timeset by said transmission timing means, said selected signal reflectingto provide a reflected return signal to said transducer means afterstriking a surface, second amplifier means having an input connected toreceive reflected return signals from said transducer means and havingan output providing an amplified reflected return signal, detector meansfor detecting signals at the output of said second amplifier means,signal discriminator means for determining the duration of signals atthe output of said second amplifier means in relation to a preselectedtime period, said signal discriminator means rejecting signals of lessthan said preselected time period, indicator means connected to theoutput of said signal discriminator means, said indicator meansincluding power drive means for driving an indicator to indicate whEn areflected signal has been received by the transducer and which has notbeen rejected by said signal discriminator means during each revolutionof said rotating drive means.
 2. The combination as specified in claim 1wherein said indicator means comprises a light emitting diode means, andsaid power drive means supplies current to said light emitting diodemeans.
 3. The combination as specified in claim 1 wherein said circuitmeans is mounted onto a circuit board, and said rotating drive meanscomprises a disc-like member rotating substantially parallel to andadjacent said circuit board, said signal means comprising a magnetmounted on said disc member, and said means to sense said signal meanscomprising a coil mounted on said circuit board positioned in theannular path of said magnet and in position wherein the magnetic fieldfrom said magnet passes across said coil as said disc rotates togenerate said control signal.
 4. The combination as specified in claim 3wherein said high gain amplifier means for said control signal comprisesa bias control transistor having a collector, emitter and base, meansproviding a normal bias voltage on the base of said transistor, and saidcoil being connected in the circuit to the base of said transistorwhereby voltage generated in said coil by passage of the magnet adjacentsaid coil is in series opposition to the voltage normally on said baseand whereby the collector of said transistor raises in potential when avoltage is generated in said coil.
 5. The combination as specified inclaim 4 wherein said means providing a transmission of signals throughsaid transducer comprises a high frequency oscillator, and drive meansto said oscillator, said drive means including a firstresistance-capacitor timing clock network, the change in potential atthe collector of said bias control transistor triggering action of saidfirst resistance-capacitance network.
 6. The combination as specified inclaim 1 and means to deliver a secondary signal when the return fromsaid transducer is less than a preselected time after the transmissionof the first signal through said transducer means, said means to delivera secondary signal including means to generate a signal proportional tothe time after ceasing the transmission of said first signal throughsaid transducer, comparator means to compare the signal generated bysaid means to generate said proportional signal with a selected signallevel, three input gate means delivering an output signal whenevertransmission of said transmitted signal has ceased and the signaldiscriminator gives an output prior to the time when the signal from themeans delivering said signal proportional to time equals said comparatorsignal, and separate indicator means connected to the output of saidgate means to give an indication when the gate means delivers an output.7. The combination as specified in claim 6 wherein said separateindicator means comprises an audible signal, and means connected to theoutput of said gate means to lock said audible signal on for a length oftime sufficient to be discerned by human ear.
 8. The combination asspecified in claim 6 wherein said means to develop a signal proportionalto time comprises an operational amplifier having an output proportionalto the difference between two inputs, a feedback connection between theoutput of said operational amplifier and one input thereto, capacitancemeans in said feedback connection to cause generation of an outputvoltage function from said operational amplifier means, and means toshort said capacitance means for a preselected length of time during thetransmission of a signal through said transducer at the start of eachcycle of said rotating drive means.
 9. The combination as specified inclaim 8 wherein said comparator means comprises a second operationalamplifier having differential inputs and an open loop gain output, oneof the inputs to said second operational amplifier being connected tothe output of saiD first mentioned operational amplifier, and the otherinput of said second operational amplifier being connected to anadjustable voltage source.
 10. The combination as specified in claim 9and means connected to the output of said second operational amplifiereffective to deliver a signal energizing said first indicator means fora preselected length of time whenever the second operational amplifierfirst delivers an output signal.
 11. In a water depth meter includingmeans for transmitting signals through a transducer and receivingreflected signals from a surface reflecting said transmitted signals,first means to indicate when the reflected signals are received inrelation to the time when the reflected signals were first transmittedthrough said transducer, and second means to give a warning when asignal is returned less than a preselected time after the transmissionof said signals through said transducer, said means to give said warningcomprising a first operational amplifier, said first amplifier having adifferential input, and one of said inputs being connected through acapacitance feedback loop whereby the output of said operationalamplifier is a straight line voltage function in relation to time, meansto initiate said voltage function at a preselected time in relation tothe initiation of transmission of said transmitted signal, andcomparator means to determine when said voltage function reaches apreselected level comprising a second operational amplifier having anopen loop gain output and a differential input, a first of thedifferential inputs to said second operational amplifier being connectedto receive the output from said first operational amplifier, and asecond of said inputs to said second amplifier comprising an adjustablevoltage source means, and means to deliver a warning when a reflectedsignal has been received before the comparator means delivers an output.12. The combination as specified in claim 11 and second means to operatesaid first means comprising a timing circuit tripped by an output ofsaid second operational amplifier operable to operate said first meansfor substantially the same period of time as a reflected signal operatessaid first means.
 13. The combination as specified in claim 11 whereinsaid first means comprises a light emitting means, a rotating disc meanscarrying said light emitting means, and means to initiate a transmissionof said transmitted signal at a preselected position during eachrotation of said rotating disc means, comprising a magnet member and acoil member, one mounted on said rotating disc and the other spaced fromand fixed with respect thereto, the magnet and coil being positioned todeliver a control signal each time the rotating disc rotates onerevolution.